xfsprogs: fix build with latest glibc headers

xfsprogs: fix build with latest glibc headers

glibc in rawhide has some changes...

* Tue Jan 12 2010 Andreas Schwab <schwab@redhat.com> - 2.11.90-8
- Update from master.
  - More POSIX conformance fixes.

* Mon Jan 11 2010 Andreas Schwab <schwab@redhat.com> - 2.11.90-6
- Update from master.
  - POSIX conformance fixes (BZ#11125).

which seem to break the xfsprogs build.  I'm no feature test macro
guru, but the following gets it going again for me.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>